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Significance Statement
Newly rising X-ray Free Electron Laser (FEL) sources aim to study the ultrafast dynamics in materials with fs time-resolution. Pump-probe experiments are the heart of these investigations and deploy high power ultrashort pulse Ti:sapphire laser systems to generate pump or probe pulses and for diagnostics purposes. Currently these laser systems, without compensation, show jitter in the region of 100 femtoseconds and drift in the several 100’s of femtosecond range and limit the real-time resolution of these experiments.
We have developed a sub-fs time-resolution, fully optical measurement device to monitor the timing jitter and drift of our TW-scale Ti:sapphire laser system. This allowed monitoring and correlating timing noise to external influences and to the specific design of the laser. By employing an external compensating delay stage with nano-sensors, we have achieved an rms noise of ~3fs over several hours of our measurement with the scope of extending this to reliable day-to-day operation. This implies 1mm accuracy over the total ~60 m propagation path.
Furthermore we conceptually designed a spectrally resolved cross-correlation setup to mix the output signal of our 20 mJ laser directly with the optical reference clock oscillator of the FEL machine, operating at 1550 nm. This system will allow femtosecond level timing correction of the Ti:sapphire probe laser to the FEL experiments, to enable increased resolution for the pump-probe experiments.
More information about the project and the group can be found here: https://www.psi.ch/swissfel/laser-group
Figure Legend: The graph shows the long term timing stability measurement over 10 hours. The delay motor compensated for the over 700 fs timing drift (b) and brought the jitter less than 3fs RMS level (a)
Journal Reference
Optics Express Vol. 23, Issue 23, pp. 29929-29939 (2015)
Marta ‘Csatari’ Divall1,* , Patrick Mutter1 , Edwin J. Divall1 , Christoph P. Hauri1,2
[expand title=”Show Affiliations”]- Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
- Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland * [email protected]
Abstract
Intense ultrashort pulse lasers are used for fs resolution pumpprobe experiments more and more at large scale facilities, such as free electron lasers (FEL). Measurement of the arrival time of the laser pulses and stabilization to the machine or other sub-systems on the target, is crucial for high time-resolution measurements. In this work we report on a single shot, spectrally resolved, non-collinear cross-correlator with sub-fs resolution. With a feedback applied we keep the output of the TW class Ti:sapphire amplifier chain in time with the seed oscillator to ~3 fs RMS level for several hours. This is well below the typical pulse duration used at FELs and supports fs resolution pump-probe experiments. Short term jitter and long term timing drift measurements are presented. Applicability to other wavelengths and integration into the timing infrastructure of the FEL are also covered to show the full potential of the device.
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